EBNA2 and EBNA-LP: The Earliest Viral Latency Proteins

EBNA2 and EBNA-LP are the earliest expressed viral latency proteins following Epstein-Barr virus (EBV) infection of B cells and are essential for cellular transformation and immortalization. Both proteins are co-expressed during latency IIb and III states and exhibit temporal regulation from viral promoters Wp to Cp during the initial 24 h of infection. Recent advances have fundamentally transformed our understanding of EBNA2's mechanisms of action, revealing its ability to undergo liquid-liquid phase separation to form nuclear condensates that reorganize host chromatin topology and create accessible chromatin domains. EBNA2 functions through sophisticated partnerships with cellular transcription factors including RBP-Jκ and EBF1, exploiting preexisting B cell transcriptional networks by targeting super-enhancers and establishing new enhancer-promoter contacts that alter over 1700 chromatin looping interactions genome-wide. The protein's unique structural features, including the virus-specific N-terminal END domain and intrinsically disordered regions critical for phase separation, represent potential therapeutic targets. Importantly, EBNA2 has emerged as a critical factor in autoimmune disease pathogenesis, with specific alleles conferring differential multiple sclerosis risk through binding at autoimmune susceptibility loci. While historically viewed as an EBNA2 coactivator, EBNA-LP has been revealed to have essential EBNA2-independent functions, serving as a key viral antagonist of restriction factors Sp100 and Sp140L to prevent innate antiviral sensing and enable successful viral genome establishment. EBNA-LP regulates chromatin architecture through interactions with YY1 and modulates transcription factor-binding accessibility at cellular genes, while both proteins cooperate at EBV super-enhancers to control target gene networks essential for B cell transformation and survival.